The present invention relates to apparatus for laying submarine pipeline, and more particularly, to a two axis pivoting pipelaying device suitable for laying deep water submarine pipeline from a surface vessel.
In general, the dual axis pivoting pipe layer provides a tool which permits the assembly of a string of pipe and the laying of the pipe string on the ocean bottom. A specific use of the dual axis apparatus permits the assembly and deployment of a submarine pipeline from a tanker moored offshore for transfer of fuel oil from the tanker to the shore.
Prior systems for laying pipe from a ship to shore, or for merely laying an undersea pipeline, require the alignment of the ship or pipe laying vessel in the direction of the pipe lay, and assembling and laying the pipe with a pipe tensioner and a stinger. The pipe tensioner squeezes down on the pipe as it plays out at a controlled rate.
The stinger is a device which prevents the pipe from bending sharply, and it supports the pipe for approximately 300 feet before permitting the natural catenary of the pipeline being layed to control. The pipe tensioner is very heavy and expensive while the stinger, also large and expensive, is very difficult to stow and deploy. The prior art devices used for pipe laying do not have two axis pivoting and the pipe laying vessel must be aligned with the pipeline.
Use of the present invention avoids problems found in prior systems by permitting the pipe laying vessel to be in virtually any alignment position including being perpendicular to the pipeline being layed, thus allowing pipe laying from a vessel whose alignment position varies with ocean currents. In addition, the present invention eliminates the need for a stinger (ramp) and a tensioner when laying pipe.